1. Field of the Invention
The present invention relates to a method and apparatus for dermatological tissue treatment, and more particularly, to a method and apparatus comprising a combination of a light source, a handpiece, and an optical means for measurement of the handpiece motion utilized for controlling the tissue treatment.
2. Description of the Related Art
Lasers and other intense light sources are used for various types of tissue treatment, including dermatological tissue treatment. During dermatological tissue treatment utilizing light, a light beam irradiates the skin surface of a patient. Generally, lasers that are used for such treatment operate at a wavelength that is absorbed by one of the natural chromophores in the skin, such as water. In the case of water as the primary chromophore, cellular and interstitial water absorbs light energy and transforms the light energy into thermal energy. The transport of thermal energy in tissues during treatment is a complex process involving conduction, convection, radiation, metabolism, evaporation and phase change that vary with the operational parameters of the light beam. It is important in such procedures not to damage tissue underlying or surrounding the target tissue area. If the light beam optical operational parameters, such as wavelength, power, the intensity of the light, pulse duration, rate of emission, etc. are properly selected, cellular and interstitial water in the patient's skin is heated causing temperature increases that produce a desired dermatological effect. Conversely, improper selection of the optical operational parameters can result in undertreatment or overtreatment of the tissue. Therefore, it is desirable to accurately control optical operational parameters used in the treatment so that the light is delivered to the tissue in a controlled manner. A variety of devices have been proposed that intelligently control laser beam power, intensity, duration, etc. However, as will be discussed in greater detail below, application of these devices have significant disadvantages.
Known devices for dermatological tissue treatment include a hand-held delivery apparatus, sometimes referred to as a handpiece. A handpiece is the preferred means by which physicians apply treatment to tissue. During treatment, the handpiece emitting light is moved by a physician's hand along the tissue to be treated. Treatment level from such a device is typically set in advance by manually selecting the light beam operational parameters. The operational parameters, which for example include power level, energy, pulsation rate, temperature, light intensity, and current, determine the degree of treatment of the entire treatment process.
One disadvantage of some of the existing handpiece apparatuses is that they require strict precision in positioning of the handpiece and application of controlled movement in order to stay within limits of safe, uniform and efficacious treatment. Theoretically, strict precision can be achieved with a high degree of skill, attention and dexterity from the treating physician. In a real procedure, however, manual application and control of the handpiece can easily result in non-uniformity of treatment due to imprecise or involuntary movements of the human hand and/or uneven tissue surfaces. This often results in either some areas of the targeted tissue being under-treated, or causes some areas to be over-treated.
A typical approach of known handpieces is to produce a macroscopic, pulsed treatment beam that is manually moved from one area of the skin to another in a patchwork like manner in order to treat a larger region of skin tissue. Such an approach has the disadvantage of producing artifacts and sharp boundaries associated with the inaccurate positioning of the individual treatments with respect to the treated skin surface.
Another disadvantage of known handpieces is that, as discussed above, the laser operational parameters defining the selected level of treatment are typically pre-set once for the entire course of treatment. The individual tissue properties of each patient are factored-in based on a preliminary tissue assessment prior to the treatment and the treatment can proceed using the predetermined operational parameters.
For example, some existing handpiece apparatuses provide feedback indicating to the physician the rate of the handpiece movement which allows the physician to adjust the treatment speed. But this handpiece apparatus requires the physician to treat at a pre-selected rate of motion. The disadvantage of this apparatus is that it restricts the physician to a single treatment speed. In large flat areas, such as the cheek, it is desirable to treat at a high speed. In highly contoured areas, such as the lip, it is desirable to treat at a lower speed. Restricting the physician to a pre-selected rate of motion limits the flexibility of the physician when treating regions, such as the face, that include both large flat areas and highly contoured areas that are in close proximity. Additionally, if the speed of the handpiece changes during the treatment procedure, the apparatus does not provide for automatic adjustment of its operational parameters to compensate for the changed rate of movement, leading to uneven treatment.
The application of robotic means used in the field of dermatological or cosmetic surgery could overcome the limitation of human imprecision. However, one disadvantage of typical conventional robotic apparatuses is that they lack the necessary direction and judgment in treatment that a physician provides. Although robotics is precise, it is not typically intelligent enough to make complex choices or react to unforeseen circumstances during treatment. Additionally, robots deprive a physician of discretion in an aesthetic sense.
Another disadvantage of the typical conventional robotic apparatus is that the full treatment may require complete immobilization of the patient. Alternatively, a sophisticated image stabilization system must be employed to compensate for patient's movement. It is still another disadvantage of such robotic apparatuses that they are bulky and cannot be easily moved into treatment positions in relation to the areas allowing little room for movement. Rather, a tissue surface to be treated has to be brought into a specific position in relation to the apparatus before treatment can take place.
A disadvantage of the use of known handpieces that depend on optical resolution of features on the skin is that in areas where there are few features, indistinct features, or no features on the skin, inconsistent results can be obtained. This is particularly true when a window in the optical field of a motion sensor element is placed in contact with the skin or in contact with an ointment applied to the skin. The application of a dye such as FD&C Blue No. 1 can solve these problems, but the application of such visible dyes can be an inconvenient extra step in a treatment process and the visible dyes can be time consuming to remove.
Thus, there is a need for method and apparatus which reduce some or all of the problems associated with the existing laser-induced handpieces apparatuses and robotics.